I know I'm always going on about utility scale energy storage and I know I'm often talking
about some apparently new revolutionary new concept that a research team somewhere in the
world has managed to get to perform flawlessly in a small scale mock-up in their laboratory,
which they think entitles them to use words like breakthrough and game changer in their
press releases. And I know that annoys some of you. So what I thought I'd do today is bring you
news of an apparently revolutionary concept whose creators have managed to get to perform very well
in a small scale mock-up in their laboratory and which they think
could become a real breakthrough game changer in utility scale energy storage.
Hello and welcome to Just Have a Think. It's probably worth a quick recap on where
we're actually at with grid scale energy storage at the moment. So,
wind and solar - both intermittent energy sources, yada yada, we all know that part by now I think.
And I think most people also now understand that we need some sort of energy storage
to capture electrons when they're available from mother nature
and give them back to our grids when the sun's not shining or the wind's not blowing. Pumped hydro
is actually the biggest contributor right now accounting for 95 percent of all utility scale
energy storage in the United States and set to increase rapidly all over the world
especially in good old China, which according to the International Energy Agency already
accounts for 50 percent of all global pumped hydro deployments. But pumped hydro is very expensive,
and of course is limited to areas with a steep incline and enough space for a reservoir-sized
body of water at the top and bottom of a hill. Generally speaking all the new technologies being
developed are designed either as a competitor for or complement to lithium-ion batteries,
so why do we need an alternative to these things then? Surely they've been working pretty well in
small devices and electric vehicles for years and they've been proven to work at very large scale as
well. All true, but at utility scale lithium-ion batteries are only being used for a discharge time
of about four to six hours and that's because although they're brilliant and most cost effective
at releasing energy instantaneously and over relatively short periods for stabilizing
grids through frequency regulation, over longer durations for providing scheduled baseload style
electricity overnight or over a few days where you don't really need instantaneous response times,
the economics of lithium-ion just don't stack up so well. And that's why developers all over
the place are scrabbling to bring more cost effective longer duration solutions to market,
many of which we've covered on this channel. So what's this latest revelation all about then? Well
how do I put this? It's an electrically conductive gloop with the consistency of molasses... now hang
on! Don't click the back button just yet! Stay with me here. This system comes from a team at
Massachusetts Institute of Technology or MIT, which is a fairly highly regarded academic
institution, so it might not be as hair brained as it initially sounds. The gloop is the key element
in something called a semi-solid flow battery, and the full explanation of how it works was published
in this paper in November 2021. Flow technology has been around for a while now. It's a kind
of cross between a battery and a fuel cell and it's very easily scalable. The typical existing
setup consists of two tanks of electrolyte liquid containing solutions of vanadium.
The vanadium ions in each tank have different chemical configurations so that one tank acts
as a positive electrolyte and the other tank acts as a negative electrolyte. In between them there's
a cell stack. The solutions from each tank are pumped into the cell stack where they're separated
by a thin membrane. As the system discharges, the ions in the negatively charged solution release
an electron in a process called oxidation. Those electrons move towards an electrode in the cell
stack and go out through a circuit to do their useful electrical work before returning to another
electrode on the other side of the stack. That electrode feeds the electrons into the positively
charged solution which is happy to receive them via a process known as reduction. Hence the name
Redox. The process frees up positively charged hydrogen ions which flow across the membrane to
maintain the charge balance. The whole thing is completely reversible so that the system
can be recharged through hundreds of cycles. The duration time that flow batteries can discharge,
releasing the stored electricity, is determined by the physical volume of positively and negatively
charged electrolyte solutions streaming through the stack. In theory as long as those solutions
keep flowing, reacting and converting the chemical energy to electrical energy, the battery systems
can keep providing electricity. But while flow battery technology in principle has shown
potential for at least a decade, the vanadium it uses is a scarce and expensive resource,
and the base for the electrolytes is a pretty nasty toxic acid solution. Those issues combined
with a somewhat uneven performance have slowed the implementation of these systems into electricity
grids around the world. The team at MIT led by mechanical engineering PhD grad Thannia Malai
Narayanan has come up with a rechargeable flow battery based on a combination of abundant and
very low cost manganese dioxide and zinc. The manganese dioxide particles are contained in a
kind of paste along with electrically conductive carbon black. The gloop arrives at the stack
where it reacts with a conductive zinc solution or zinc plate to cause the electrochemical reaction.
There are very good reasons for using this kind of semi-solid material instead of just using a
liquid. You get a much higher energy density for a start, plus the paste has a higher surface area on
which the all important electrochemical reactions can take place. But there are drawbacks as well.
Because flow batteries by definition rely on flow of fluids around the system you need a pump
to circulate everything, and pumping a paste is a lot more difficult than pumping a liquid. It
generally requires a more expensive reciprocating pump instead of the cheaper centrifugal pumps that
are commonly used for existing flow batteries. There may also be a need for more pumps at various
points in the system and deeper channels to allow this pasty viscoplastic material to flow as freely
as possible. And the whole thing requires way more energy input, which of course drives up
the overall cost of the system. MIT professor of engineering Gareth McKinley, who's been heavily
involved in the project, pointed out another pitfall as well, explaining "these systems have
to be able to flow under reasonable pressures but also have a weak yield stress so that the active
manganese oxide particles don't sink to the bottom of the flow tanks when the system isn't being used
as well as not separate into a battery oily clear fluid phase and a dense paste of
carbon particles and manganese oxide". All of which sounds a bit tricky to me!
So the team embarked upon a long journey of experimentation and testing to see if they could
find an optimal combination of all the elements in the mix, not just from a physical mechanical
and operational performance point of view, but also carefully considering the economic viability
of the system calculating what's known as the levelized cost of storage or LCOS versus other
storage technologies using what the research is referred to as techno-economic analysis
based on previously published industry data. Another team member, Emre Gençer,
who creates detailed economic models of emergent energy systems at MIT's energy initiative program,
explained "assessing the cost and performance of early technologies is very difficult, and this was
an example of how to develop a standard method to help researchers at MIT and elsewhere. One message
here is that when you include the cost analysis at the development stage of your experimental work
you get an important early understanding of your project's cost implications". Gençer and Narayanan
compared their zinc manganese battery to a set of equivalent electrochemical battery and hydrogen
backup systems, looking at the capital cost of running them at durations of 8, 24 and 72 hours.
What they found was that for battery discharges longer than a day their semi-solid flow battery
was more cost effective than both lithium-ion batteries and vanadium redox flow batteries, even
after the heavy cost of pumping the viscoplastic slurry from tank to stack was factored in.
Again though, having said all that, these sorts of developments are not trying to
supersede existing technologies like lithium-ion batteries and they wouldn't be able to compete
with lithium-ion batteries at the shorter duration time scales anyway. What they're really designed
to be is a fully complementary addition to fill what is currently a gap between short and very
long duration energy storage solutions. And the great advantage of a system like a flow battery
is that it's very easily scalable as I mentioned earlier. If you want more storage
you simply add more tanks to the existing setup. The only limitation is space,
which is why technology like this is unlikely to find its way into domestic situations
any time soon. It's much better suited for large centralized utility scale grid systems. Narayanan
reckons that their research has also indicated other chemistries that could be developed using
the semi-solid flow battery method, so who knows we could be seeing various versions of this
novel technology on the electricity grids of the future as societies around the world come to rely
more and more on intermittent renewables like wind and solar. I'm quite sure many of you will have
a view on this technology and perhaps even on the wider topic of intermittent renewables and energy
storage in general. If you do, or if you work in the industry and you have some insights you can
share, then why not jump down to the comments section below and leave your thoughts there.
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